1. Field of the Invention
The present invention relates to a battery, and more particularly to a film-sealed non-aqueous electrolyte battery including a non-aqueous electrolytic solution.
2. Description of the Related Art
Requirements for size reductions of various electronic devices have been on the increase. The importance for size reduction of the battery for realizing the size reductions thereof has also been on the increase. It is effective that a battery element for generating a power is accommodated in a thin film outer case, such as a laminated film case.
The laminated film case comprises laminations of metal foils or sealing polymer resin layers. The laminated film case may seal the battery element by a heat-application. A high reliability of sealing the sealing portions of the laminated film case is necessary for isolating the battery element from the atmosphere and also preventing leakage of the electrolyte of the battery element.
The sealing reliability is particularly important for the battery including a non-aqueous electrolyte. If the sealing is imperfect to allow an entry of moisture from the outside of the battery case, then the electrolyte is deteriorated by the moisture, whereby the battery performance is deteriorated. Some batteries have such a structure that metal plate-shaped lead terminals extend from the battery element through the sealing portion of the laminated film case toward the outside of the case. In this case, an adhered area between the metal plate-shaped lead terminals and a sealant layer of the laminated film case is likely to be deteriorated in sealing reliability to cause a peel between them and form a leak path.
The leak path is likely to be formed through the deteriorated adhered surfaces of the sealant layer and the lead terminals for the following two reasons. First, it is generally difficult to obtain a strong adhesion between the metal surface and the polymer resin surface. Second, lithium salts of inorganic fluoride, for example, LiPF6 have been used frequently for electrolyte salt of the non-aqueous electrolyte, and are likely to be decomposed to generate a fluorine acid which is capable of corrosion of metal, whereby the lead terminal surfaces arc corroded, resulting in a deterioration in adhesion between the sealant layer and the lead terminals.
In order to counter-measure the above problems, it was proposed that surface-treated lead terminals are used for the film-sealed non-aqueous electrolyte battery. Japanese laid-open patent publication No. 10-312788 discloses chromate-treatment to surfaces of the lead terminals to form anti-corrosion coating films on the surface of the lead terminals. The anti-corrosion coating films may prevent corrosion by the fluorine acid, for obtaining a desirable high sealing reliability.
The chromate-treatment is superior to other surface treatments in view of its anti-corrosion property. The chromate treatment is carried out by using hexavalent chromium (Cr(VI)) which is harmful substance, for which reason in the environmental viewpoint, it is desirable to use chromium-free surface treatment.
As described above, it is desirable that the anti-corrosion coating film is formed on the lead terminal surface to improve the reliability of adhesion between the sealant layer and the lead terminal, thereby obtaining a desirable high sealing reliability particularly of the film-scaled non-aqueous electrolyte battery. If the lead terminal is electrically connected to the battery element or an external device by a cramping method, a resistance welding method, or an ultrasonic welding method, it is necessary to avoid generation of the contact resistance at the contact point. It is also necessary to prevent that the anti-corrosion coating film is dissolved into the electrolyte, resulting in a deterioration in performance of the battery.
In the above circumstances, the development of a novel film-sealed non-aqueous electrolyte battery with improved surface-treated lead terminals free from the above problems is desirable.